1. Field of the Invention
The present invention relates to a headband device, and more particularly to an adjustable headband device for a helmet that allows a user to easily adjust a headband for fitting the user's head circumference.
2. Description of Related Art
Helmets are widely used in fields of construction, motorcycling and extreme sports and is worn on a user's head for cushioning external impact on the user's head, thus to provide additional protection to the user's head.
A conventional helmet has a housing, a cushion element and a chin strap. The housing is hard and hollow. The cushion element is mounted in the housing. The chin strap is attached on opposite sides of an opening of the housing and may be tightened on a user's chin to secure the helmet on the user's head. The hard housing and the cushion element cooperate to cushion external impact. However, a size of the helmet cannot be adjusted such that the helmet may be loosely worn on and even fall off from a user' head when the size of the helmet is larger than that of the user's head. Therefore, helmet manufacturers usually produce helmets of different sizes for different users and each user needs to try different sizes of the standardized helmet, which is inconvenient and inefficient for both the manufacturers and users.
A helmet with an adjustable headband has been developed and has the adjustable headband mounted on an inner surface of the helmet. The adjustable headband has two toothed racks formed on two ends of the headband and engaging a gear located therebetween. An adjusting knob is connected to and rotates the gear to drive the toothed racks toward or away from each other, which changes an inner diameter defined by the headband looped into a circle.
To prevent a user from unintentionally increasing the inner diameter of the looped headband due to unexpected vibration or external force, a ratchet wheel and a ratchet pawl are mounted in the adjusting knob to limit the adjusting knob to only rotate in a single rotational direction that allows reducing the inner diameter of the looped headband. To increase the inner diameter of the looped headband, the adjusting knob is pushed to disengage the ratchet wheel from the ratchet pawl, and then the adjusting knob can be rotated reversely to enlarge the inner diameter of the looped headband. After the adjusting knob is released, a biasing spring pushes the adjusting knob back to its original position to re-engage the ratchet wheel with the ratchet pawl.
However, in order to enlarge the inner diameter of the looped headband of the aforementioned helmet with the adjustable headband, the user needs to simultaneously push and rotate the adjusting knob, which is inconvenient.
To overcome the shortcomings, the present invention provides an adjustable headband device for a helmet to mitigate or obviate the aforementioned problems.